1. Field of the Invention
The present invention relates to a light amount adjustment apparatus for use in an image pickup apparatus, and in particular to a light amount adjustment apparatus having a plurality of plate-like light-shielding blade members and a method of manufacturing the light-shielding blade members.
2. Description of the Related Art
Generally, there are image pickup apparatuses such as digital cameras which use a diaphragm unit having light-shielding blade members mounted thereon. It is known that, like other members in an image pickup lens, when the light-shielding blade members cause undesired internal reflection, this results in degradation in image quality such as flare and ghosts. For this reason, surfaces of the light-shielding blade members are coated with a coating for light absorption so as to prevent degradation in image quality.
Also, it is known that in a diaphragm unit having light-shielding blade members, degradation in image quality such as ghosts occurs due to reflection on end faces of the light-shielding blade members which form an aperture and are parallel with an optical axis. For this reason, the end faces of the light-shielding blade members are also coated with a coating for light absorption, or the end faces of the light-shielding blade members are formed into complicated shapes so as to prevent degradation in image quality.
For example, there has been proposed a means for making end faces of light-shielding blade members which form an aperture thin-walled to a sufficient degree by injection molding so as to prevent internal reflection on the end faces (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. 2006-84658).
Also, there has been proposed a means for forming end faces of light-shielding blade members which form an aperture in a stepwise or steplessly curved pattern to make the end faces of the light-shielding blade members thin-walled to the extent possible so that regions causing harmful back reflection in the end faces of the light-shielding blade members which form the aperture and are parallel with the optical axis can be reduced so as to reduce degradation in image quality such as flare and ghosts (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. 2002-229095).
However, when light-shielding blade members are formed by injection molding, it is necessary to make end faces of the light-shielding blade members thin-walled so that the end faces of the light-shielding blade members can be small. To this end, resin input pathways provided in a mold for injection molding are formed to be extremely narrow, and it is thus necessary to prevent resin from being uncharged and also prevent burrs from being formed due to excessive charge of resin. For this reason, injection molding performed so as to make end faces of light-shielding blade members thin-walled is accompanied with a difficulty in determining injection molding conditions.
Further, when light-shielding blade members are formed by injection molding, end faces of the light-shielding blade members are formed in a stepwise fine pattern comprised of a plurality of steps or steplessly curved fine pattern by injection molding. To this end, resin input pathways provided in a mold for injection molding are formed to be extremely narrow, and it is thus necessary to prevent resin from being uncharged and also prevent burrs from being formed due to excessive charge of resin. For this reason, injection molding performed to form end faces of light-shielding blade members in a stepwise fine pattern comprised of a plurality of steps or a steplessly curved fine pattern by injection molding is also accompanied with a difficulty in determining injection molding conditions.